A catheter is a slender, hollow tube which is inserted into a body passage, vessel or cavity. Among other things, catheters are used to infuse fluids into a patient through an artificial opening in the patient's body. For example, intravenous fluid is often infused by inserting a catheter through the skin at an entry site and into a blood vein, and injecting the fluid into the body by passing it through the catheter.
When a patient loses a significant amount of blood, or is exposed to surgery or anaesthesia for long times, body temperature may drop. In such situations, heated fluids may be infused in order to raise the body temperature. However, the maximum temperature of the heated fluid is ordinarily about 41.degree. C., to avoid burns or other damage to the blood tissue or internal organs.
It has recently been discovered that relatively hot infusion fluids can significantly reduce the recovery time of patients who suffer from such temperature losses, provided that the temperature of the blood stream after mixing is not greater than 41.degree. C. The temperature of the fluids can be about 50.degree.-100.degree. C.
There is a need for a catheter to provide rapid mixing of hot fluids with the bloodstream in a controlled fashion that prevents the mixed blood from exceeding 41.degree. C. Such a catheter would also require thermal isolation from entry site tissues to prevent tissue burns.
Accordingly, one object of this invention is to provide new and improved patient warming methods and apparatus.
Another object is to provide new and improved control systems which accurately maintain desired temperatures and flow rates when relatively high temperature fluids are infused through an opening in a patient's body.
Still another object is to provide new and improved catheters for infusing relatively high temperature fluids into a patient's body, without excessive entry site or endothelial burning.